Aneuploidies involving chromosomes 21, 18, 13, X and Y account for over 95% of all chromosomal abnormalities in live-born infants. Prenatal diagnosis of these disorders is usually accomplished by cytogenetic analysis of amniotic or chorionic cells but this is a lengthy procedure requiring great technical expertise. In this paper, we assess the diagnostic value of using a quantitative fluorescent polymerase chain reaction (PCR) suitable for the simultaneous and rapid diagnosis of trisomies 21 and 18 together with the detection of DNA sequences derived from the X and Y chromosomes. Samples of DNA, extracted from amniotic fluid, fetal blood or tissues, and peripheral blood from normal adults were investigated by quantitative fluorescent PCR amplification of polymorphic small tandem repeats (STRs) specific for two loci on each of chromosomes 21 and 18. Quantitative analysis of the amplification products allowed the diagnosis of trisomies 21 and 18, while sexing was performed simultaneously using PCR amplification of DNA sequences derived from the chromosomes X and Y. These results indicate the advantages of using two sets of STR markers for the detection of chromosome 21 trisomies and confirmed the usefulness of quantitative fluorescent multiplex PCR for the rapid prenatal diagnosis of selected chromosomal abnormalities.